14. Longest Common Prefix

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14. Longest Common Prefix

Description

Write a function to find the longest common prefix string amongst an array of strings.

If there is no common prefix, return an empty string "".

Example 1:

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Input: strs = ["flower","flow","flight"]
Output: "fl"

Example 2:

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Input: strs = ["dog","racecar","car"]
Output: ""
Explanation: There is no common prefix among the input strings.

Constraints:

  • 1 <= strs.length <= 200
  • 0 <= strs[i].length <= 200
  • strs[i] consists of only lowercase English letters if it is non-empty.

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    string longestCommonPrefix(vector<string>& strs) {
        int res = INT_MAX;
        for (int i = 0; i < strs.size() - 1; i++) {
            res = min({res, (int)strs[i].size(), (int)strs[i + 1].size()});
            for (int j = 0; j < res; j++) {
                if (strs[i][j] != strs[i + 1][j]) {
                    res = j;
                    break;
                }
            }
            if (!res) {
                return "";
            }
        }
        return strs[0].substr(0, res);
    }
};

Another solution:

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class Solution {
public:
    string longestCommonPrefix(vector<string>& strs) {
        int j;
        for (j = 0; j < strs[0].size(); j++) {
            for (auto& str : strs) {
                if (j == str.size() || strs[0][j] != str[j]) {
                    return strs[0].substr(0, j);
                }
            }
        }
        return strs[0];
    }
};